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Is street lighting bad for birds?

Sent in by Kate Morgan, Lichfield

Street lighting can be advantageous to some birds but it can also have adverse effects. Artificial lighting can trick birds into thinking that the days are longer, thereby allowing them to feed for longer periods. Birds have evolved their 'body-clock', similarly to ours, and artificial lighting will no doubt upset this. Day length triggers behaviour patterns such as courtship, mating, reproductive cycles, migration and moulting.

Robins are insectivorous birds that are well adapted to foraging in dim light, and will continue to feed under artificial light well into the night. Moths and other insects will be attracted to the lights, making it an ideal area for night-time feeding. With this tendency to be active at low light, robins can be easily triggered into full song by a streetlight or any kind of floodlighting. Since robins keep territories all year round, they also sing all year round. This has resulted in dozens of reports of nightingales singing in the middle of a winter’s night and other equally unlikely times and places, which have all turned out to be robins. In fact, the robin is the most common night-time songster in Britain’s towns and gardens.

However, a lot of birds have evolved to migrate at night, such as most wildfowl and swans, as well as many song birds, to avoid the majority of predators and high winds. It is thought that these night-migrating birds can become disoriented by lights, particularly in cities. They can confuse man-made lights in tall buildings with moon and starlight, which they use to navigate. This is made worse in foggy or rainy weather, and they have been known to collide with lit-up buildings. Grasshopper warblers migrate at night, and on occasion large numbers have been killed at lighthouses. On 29 August 1968, a total of 111 grasshopper warblers were found among almost 600 dead warblers on Bardsey Island, Gwynedd. 

Nocturnal birds, such as owls, have eyes adapted to low light conditions. It would make it difficult for these birds to hunt effectively in areas where there are artificial night-lights. It has also been shown that robins and blackbirds in urban areas lay their eggs up to two weeks before those in woodland. As egg-laying is timed by the seasonal change in day length to coincide with the peak times of food availability, this could cause problems in food supply for the young.

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